AI 中文总结
本文基于印度脉冲星计时阵列第2次数据，开展随机引力波背景搜索，通过贝叶斯推理等方法得到相关参数，设置振幅上限，发现需至少10年基线才能恢复目标信号。
AI 中文摘要
我们在印度脉冲星计时阵列的第2次数据发布中，开展了首次针对各向同性随机引力波背景的独立搜索，该数据包含27颗毫秒脉冲星，这些脉冲星在两个频率波段被升级后的巨米波射电望远镜同时监测，监测的最大基线时长为7.2年。在全面的单脉冲星噪声分析基础上，我们在贝叶斯推理框架内、采用噪声边缘化的最优统计量，搜索共同的不相关红噪声过程，并通过逐脉冲星缺失分析和太阳风排除切割测试结果的稳健性。在光谱指数自由的情况下，我们得到了宽泛的振幅后验分布：log₁₀A_CURN = -13.71⁺¹·⁰⁶₋₃·²⁸，未受约束的光谱指数γ_CURN = 2.98⁺³·⁶²₋₂·⁷⁰，以及共同红过程相对于无信号模型的Savage-Dickey贝叶斯因子为2.5。单极、偶极和Hellings-Downs相关性的最优统计量信噪比均与零一致。将光谱指数固定为γ = 13/3（该值由理想化玩具模型预测，该模型中背景由一群仅在 leading-order 引力辐射反作用下演化的圆轨道超大质量黑洞双星产生），我们对共同过程振幅设置了95%上限：A_GWB < 3.4×10⁻¹⁴，该上限在10°、20°和30°的太阳张角切割下保持稳定。该上限比其他运行时间更长的脉冲星计时阵列实验报告的振幅大约高一个数量级。我们还通过添加简单的色散和非色散噪声分量的模拟数据集证明，至少需要10年的基线才能开始恢复共同红噪声信号。
英文摘要
We present the first independent search for an isotropic stochastic gravitational wave background in the second data release of the Indian Pulsar Timing Array, comprising of 27 millisecond pulsars monitored simultaneously in two frequency bands with the upgraded Giant Metrewave Radio Telescope over a maximum 7.2 year baseline. Building on a comprehensive single pulsar noise analysis, we search for a common uncorrelated red noise process within a Bayesian inference framework and with the noise-marginalized optimal statistics, and we test the robustness of the result through per-pulsar dropout analyses and solar-wind exclusion cuts. Leaving the spectral index free, we recover a broad amplitude posterior, $\log_{10} A_{\rm CURN} = -13.71^{+1.06}_{-3.28}$, with an unconstrained spectral index $γ_{\rm CURN} = 2.98^{+3.62}_{-2.70}$ and a Savage-Dickey Bayes factor of $2.5$ for a common red process over the no signal model. The optimal-statistic signal to noise ratios for the monopole, dipole, and Hellings-Downs correlations are all consistent with zero. Fixing the spectral index to $γ= 13/3$, the value predicted by an idealized toy model in which the background is sourced by a population of supermassive black hole binaries in circular orbits evolving purely under leading-order gravitational radiation reaction, we place a $95\%$ upper limit on the common-process amplitude of $A_{\rm GWB} < 3.4\times10^{-14}$, stable across solar elongation cuts of $10^\circ$, $20^\circ$, and $30^\circ$. This limit lies approximately an order of magnitude above the amplitudes reported by other, longer-running pulsar timing array experiments. We also demonstrate through simulated datasets with the addition of simple chromatic and achromatic noise components that it will take at least a 10 year baseline to start recovering the common red noise signal.
